Fatigue life prediction of planet carrier in slewing reducer for tower crane based on model validation and field test

Tower cranes are used to handle heavy weights, and are typically operated at considerable heights; their slewing reducer has to support both the variable wind loads at those heights and the load resulting from inertia of the system. The analysis of such transmitted loads is extremely important in crane design, to estimate the life expectancy of the slewing reducers. If the input load was measured, the load applied to the carrier of the slewing reducer could be analyzed, its weak parts determined, and the cumulative damage rate calculated; the expected life of the carrier could then be predicted more accurately. Therefore, this study estimated the fatigue life of the reducer’s carrier, using the input load measured during normal operating conditions of the tower crane. The analysis model of the slewing reducer was verified with a static load test, and the stress profile applied to the carrier was calculated using the peak-valley load extracted from the measured input; the verified slewing reducer analysis model, the rain-flow counting method, and Miner’s rule were then used to estimate the expected life of the carrier. As a result, the rates of cumulative damage of the two weakest spots were estimated to be 22.63% and 44.95%.